Mercer's next purchase of Marlborough property was on July 28, 1737,
when he bought the three lots granted in 1691 to George Andrews from
Andrews' grandson, John Cave. Meanwhile, he began large-scale
acquisitions of lands elsewhere. By 1733 he had acquired an aggregate of
8096 acres in Prince William County. In addition, he obtained a "Lease
for three Lives" on three large tracts belonging to William Brent,
adjoining Marlborough, so that he controlled virtually all of Potomac
Neck.[63]
Thus, after 1730 we find Mercer's fortune already well established and
increasing. No longer a youthful trader plying the Potomac in his sloop,
he was now a gentleman planter and influential lawyer. He lived in a new
house, owned some parts of Marlborough, and was building "improvements"
on others. Almost overnight he had become a landed proprietor.